Looks like a race to see who can be more progressive. At a rally in Harlem Saturday, Mayor-elect Bill de Blasio promised, “We are going to get on with a very, not only progressive, but aggressive agenda.”

Meanwhile, Crain’s New York Business reports that the Council’s Progressive Caucus — which is about to grow in size come Jan. 1 — has enlisted a top union official to negotiate on its behalf in the battle to select a new speaker, the city’s second-most-powerful job.

The official tapped to represent the caucus during negotiations for speaker is Alison Hirsh, political director of the powerful building-workers union, 32BJ SEIU. Hirsh is also a former chief of staff to serial sexual harasser Vito Lopez. In addition to sitting at the table with the county bosses who will decide the new speaker, she will round up votes for the caucus’s preferred candidate once it settles on one.

Just who that candidate will be hasn’t yet been decided. The early favorite seems to be Melissa Mark-Viverito (D-Man.), who’s backed by the health-care-workers union.

Hirsh, of course, is playing a dual role here. On the one hand, she negotiates on behalf of the council’s progressive caucus. On the other hand, she’s still a union lobbyist who will be seeking to persuade the same caucus (and other members of the council) to do Big Labor’s bidding. Under a Mayor de Blasio, this is not so much a conflict of interest as a confluence of interests.

In short, a larger and stronger progressive caucus within the council effectively means unions will be calling many of the shots.

And high atop Labor’s wish list is $8 billion in back raises the unions want for the years their members worked without a contract, money the city simply does not have.

On Saturday, de Blasio complained it will not be “easy” to enact his progressive agenda because “powerful forces” are mobilizing against him. But it looks to us as though the most powerful interests have already mobilized — and they are all playing for the progressive team.